Locking pliers are well known in the art. These devices have two jaws that may be locked on an object. The over-center locking mechanism is achieved by two handles, a fixed jaw on one of the handles, a movable jaw, a pivoting link between the handles, and an over-center spring between the movable jaw and the fixed jaw handle that together cooperate to lock the jaws on a work piece when the handles are forced together. The over-center mechanism includes a micro adjustment screw that controls the opening of the jaws over a limited range to accommodate articles of different sizes within the range and permits the over-center mechanism to lock. An example of such locking pliers is shown in U.S. Pat. No. 4,730,524 to Petersen that also includes a summary of the many Petersen Vise-Grip patents.
In addition to the micro adjustment screw for setting up the jaw spacing, some locking pliers include macro jaw opening mechanisms to allow use on a much wider range of work pieces. For example, U.S. Pat. No. 2,399,454 to Snell locates the jaw pivot in a slot in the upper jaw handle that is perpendicular to the upper jaw. The jaw pivot is adjusted along the slot by a screw with a head above the upper jaw handle. Turning the screw one way places the jaws closer together. Turning the screw the other way places the jaws further apart. Because of the fine spacing between the jaws that is possible using the screw, no separate micro adjustment screw in the handle is needed to set up the over-center locking mechanism as is found in the Peterson Vise-Grips.
U.S. Pat. Nos. 2,905,038 and 3,241,410 both to Paden have a long shank on the lower jaw holder. The lower jaw can be slid along the shank to determine the spacing between the jaws. The side of the shank has a series of teeth for holding the jaw. A pawl on the lower jaw engages any one of the teeth on the shank to hold the lower jaw in a given position relative to the upper jaw. Twenty-three positions are available on the embodiment shown in U.S. Pat. No. 2,905,038. Twenty positions are available on the embodiment shown in U.S. Pat. No. 3,241,410.
U.S. Pat. No. 3,672,245 to Hoffman is similar to Snell in that it has a slot perpendicular to the upper jaw in the upper jaw handle for holding the jaw pivot. But instead of using a screw to determine the location of the pivot in the slot, the position is determine by arcuate channels adjacent the slot for holding the lower jaw pivot ata desired spacing from the fixed upper jaw. Movement between the arcuate channels is achieved by loosening a nut on the pivot until the movable jaw can be slipped over the arcuate channels to a different set of arcuate channels. The nut is then tightened on the pivot to hold the pivot at a selected set of arcuate channels. Seven positions are available on the embodiment shown.
U.S. Pat. No. 3,981,209 to Caroff shows a locking pliers where the length of the link between the two handles is adjustable to control both the micro and macro jaw adjustment functions. Again a slot perpendicular to the upper jaw as in Hoffman and Snell is provided in the upper jaw handle. The length of the link is first adjusted to allow the pivot for the movable jaw to be moved in the slot toward or away from the fixed jaw. When the desired position is reached, the pivot is pushed into one of a plurality of teeth on the side of the slot opposite the link. The jaws are then moved around the work piece and the length of the link is further adjusted until the micro jaw adjustment is achieved that causes the jaws to lock on the work piece using the over-center principle when the handles are squeezed together. Five positions are available on the embodiment shown.
U.S. Pat. Nos. 6,578,452 and 5,022,290 both to Duffy have an upper jaw on a slide that moves in a slot in the lower jaw holder. The edge of the slide has a plurality of teeth for holding the jaw. A lock engages any one of the teeth to hold the upper jaw in a desired position with respect to the lower jaw. Three positions are available on the embodiment shown in U.S. Pat. No. 5,022,290. Thirty positions are available on the embodiment shown in U.S. Pat. No. 6,578,452.
U.S. Pat. No. 5,385,072 to Neff also has a slot in the holder for the lower jaw but moves the lower jaw in the slot instead of the upper jaw as in Duffy. Pins through the slot hold the lower jaw. The position of the lower jaw relative to the upper jaw is determined by an adjusting lever. About twelve positions are available on the embodiment shown. Jaw adjustment mechanisms are also known in non-locking pliers. For example, U.S. Pat. No. 4,581,960 to Putsch shows a pliers having two handles that cross each other and are connected together by a pivot. The pivot is attached to one of the handles and slides in a slot in the other handle to change the gap between the jaws. The sides of the slot have teeth. The pivot is mounted in a rectangular block having teeth on the sides matching the teeth on the sides of the slot. A push button on the end of the pivot is pushed to move the rectangular block out of the slot. This allows the pivot to be moved along the slot to a new position. When the push button is released, a spring on the other end of the pivot forces the rectangular block back into the slot where the teeth once again engage each other locking the pivot at a desired location. About twelve positions are available on the embodiment shown.